Terraform Quick notes -

Reference - Terraform Registry

Type of terraform providers

1. Official - Managed by terraform.
2. Verified - Managed by terraform partners.
3. Community - Managed by users.

Various files can be created

1. main.tf - Main configuration file containing resource definition.
2. variables.tf - Contains variable declarations.
3. outputs.tf - Contains outputs from resources.
4. provider.tf - Contains provider derfinition.

Terraform Variables

1. string - a sequence of Unicode characters representing some text, like "hello".
2. number - a numeric value. The number type can represent both whole numbers like 15 and fractional values like 6.283185.
3. bool - a boolean value, either true or false. bool values can be used in conditional logic.
4. list (or tuple) - a sequence of values, like ["one", "two"]. Elements in a list or tuple are identified by consecutive whole numbers, starting with zero.
5. map (or object) - a group of values identified by named labels, like {name = "Mabel", age = 52}.

Terraform loads variables in the following order, with later sources taking precedence over earlier ones:

• Environment variables
• The terraform.tfvars file, if present.
• The terraform.tfvars.json file, if present.
• Any *.auto.tfvars or *.auto.tfvars.json files, processed in lexical order of their filenames.
• Any -var and -var-file options on the command line, in the order they are provided. (This includes > variables set by a Terraform Cloud workspace.)

Specify explicit dependency

• depends_on - depends_on = [(Resource type).(Resource name)]

Lifecycle block

The arguments available within a lifecycle block are create_before_destroy, prevent_destroy, ignore_changes, and replace_triggered_by

• create_before_destroy - bool
• prevent_destroy - bool
• ignore_changes - list of attribute names
• replace_triggered_by - list of resource or attribute references

Main commands:

• init - Prepare your working directory for other commands
• validate - Check whether the configuration is valid
• plan - Show changes required by the current configuration
• apply - Create or update infrastructure
• destroy - Destroy previously-created infrastructure

All other commands:

• console - Try Terraform expressions at an interactive command prompt
• fmt - Reformat your configuration in the standard style
• force-unlock - Release a stuck lock on the current workspace
• get - Install or upgrade remote Terraform modules
• graph - Generate a Graphviz graph of the steps in an operation
• import - Associate existing infrastructure with a Terraform resource
• login - Obtain and save credentials for a remote host
• logout - Remove locally-stored credentials for a remote host
• output - Show output values from your root module
• providers - Show the providers required for this configuration
• refresh - Update the state to match remote systems
• show - Show the current state or a saved plan
• state - Advanced state management
• taint - Mark a resource instance as not fully functional
• test - Experimental support for module integration testing
• untaint - Remove the 'tainted' state from a resource instance
• version - Show the current Terraform version
• workspace - Workspace management